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Thread: Serious incident (hyperoxia) when 2 cells fail simulatenously and identically

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    Re: Serious incident (hyperoxia) when 2 cells fail simulatenously and identically

    Quote Originally Posted by Paul S  View Original Post
    I think you're overstating the diagnostic usefulness of a dil flush.

    You're at 30 meters (4 ATM) and have air diluent. Your cells are reading 2.10 - 1.20 - 1.25, so you do a dil flush. They all drop to 0.89 - 0.80 - 0.85. We're now on known gas and the readings look about right for it, but its not clear what the problem is (at least to me). Is cell 1 running high or are 2&3 both limited? "It can't be 2 AND 3 surely, they've been so close to each other the whole dive. "
    .
    I agree, the dil flush is not the end all be all and I apologize if it came off that way. Two cells failing from current limiting at the same range is a nightmare scenario. Hopefully you'd catch it at your 6m O2 flush during descent but no guarantees.

    Just thinking outloud here but if you had planned the bottom PPO2 of your bailout at 1.4 or so (35% o2 in your case) you could technically test for current limiting to a point higher than the typical setpoint of 1.2 during the deep portion of your dive with an offboard dil flush. Food for thought but not really practical in most cases.

    The question is, do you continue your dive on CCR with ONE (perceived) failed cell? In this case a Yes answer could potentially save you.
    Last edited by tmccar1; 11th December 2012 at 16:10.

  2. #32
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    Re: Serious incident (hyperoxia) when 2 cells fail simulatenously and identically

    Quote Originally Posted by Paul S  View Original Post
    I think you're overstating the diagnostic usefulness of a dil flush.

    You're at 30 meters (4 ATM) and have air diluent. Your cells are reading 2.10 - 1.20 - 1.25, so you do a dil flush. They all drop to 0.89 - 0.80 - 0.85. We're now on known gas and the readings look about right for it, but its not clear what the problem is (at least to me). Is cell 1 running high or are 2&3 both limited? "It can't be 2 AND 3 surely, they've been so close to each other the whole dive. "

    Unless you hear the solenoid it's easy to make the decision that cell 1 is bust and acting odd, and if we're full eCCR then we're going back hyperoxic very soon. I'm thinking the smart choice, if your set on staying on the loop, might be to bring the set-point into a range we can verify, which in this case would be about 0.85. We now know the cells work at that level.
    Paul - have you done a Dil flush on an OTSCL eCCR?

    Its amazingly effective when done correctly. It also requires a fast sampling electronics package. Ie. - not much benefit in understanding whats going on in replacing the loop gas quickly if the electronics dont read and reflect it on your display.

  3. #33
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    Quote Originally Posted by Chris at Silent World  View Original Post
    Paul - have you done a Dil flush on an OTSCL eCCR?
    No. I haven't.

    Its amazingly effective when done correctly. It also requires a fast sampling electronics package. Ie. - not much benefit in understanding whats going on in replacing the loop gas quickly if the electronics dont read and reflect it on your display.
    I don't understand your point. What has the speed of a flush got to do with what information it gives you?

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    Re: Serious incident (hyperoxia) when 2 cells fail simulatenously and identically

    Quote Originally Posted by jaksel  View Original Post
    Earlier this year a serious CCR-related incident occured to a diver I know (he wishes to remain anonymous). On a dive to 52 meters, using an APD Inspiration, two out of 3 cells failed simulatenously and with closely matching cell voltages, while the third cell continued to operate properly. This caused the setpoint controller to reject the single functioning cell and instead derive its measured ppO2 from two current-limited cells.

    Thanks for posting, glad it worked out OK.

    Clearly diver error though. The diver was given a warning that they had bad cells.

    Cell warnings are not normal on a Vision. They are telling you you have a problem. I dont get them on any vision when I change to high SP even on a fast hot drop. I do get them when the cells are on their way out though. The warning at SP change can also be caused when you have good cells by not breathing the loop around enough when it switches or by having too much loop volume. I find that exhaling out the nose at switch will prevent it.

    Theres also a training consideration here. At what point was he taught to bail out? I teach that a spike above 1.6 needs to be flushed immediately and above 1.8 you need to be off the loop regardless of what you think about cell health.

    A quick swap to the OCB or offboard - sanity breaths and then Dil flush could save your life in this kind of scenario.

    Also - I have never seen cells simultaneously 'fail' as you put it. They often give you ample pre-warning that they are becoming current limited. In your friends case the electronics were also doing it and helping you via the 'CELL WARNING' and beeping on the vision.

    Testing cells at 1 Bar is not a complete check as Martin Parker has confirmed on the boards in the past. All you are confirming is that your cells output xyz Mv in air or 02 at 1 bar. You need to compare that to higher pressures and track the output against a table of predicted outputs. Were these cells tested in a cell checker such as the remobulator by JM or Narked at 90's cell checker?

    It surprises me that thousands of people dive the vision electronics around the world and seem to have no knowledge that it has more software to mitigate this issue than you would think. A bit of PR from AP might be in order :)

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    Question Re: Serious incident (hyperoxia) when 2 cells fail simulatenously and identically

    Hi Guys. I dive a meg mCCR. There are no alarms no ADV or BOV and 1no. Handset. In the event all my cells failed, I can rely on my HUD to maintain my ppo2, without any worries or complications. And have full confidence while I call the dive. stand alone computer handles ascent and stops. Job done

    Couldn't you just, flush, switch to manual and monitor your HUD?? Now I'm not familiar with eCCR so im not sure. Just thought id ask the question.

    Andy

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    Re: Serious incident (hyperoxia) when 2 cells fail simulatenously and identically

    Your HUD relies on your cells to give you ppO2 information. Failed cells = failed HUD. What you suggest cannot work.



    Quote Originally Posted by Nuclear Penquin  View Original Post
    Hi Guys. I dive a meg mCCR. There are no alarms no ADV or BOV and 1no. Handset. In the event all my cells failed, I can rely on my HUD to maintain my ppo2, without any worries or complications. And have full confidence while I call the dive. stand alone computer handles ascent and stops. Job done

    Couldn't you just, flush, switch to manual and monitor your HUD?? Now I'm not familiar with eCCR so im not sure. Just thought id ask the question.

    Andy

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    Re: Serious incident (hyperoxia) when 2 cells fail simulatenously and identically

    About two weeks ago I had a cell starting to read high. Pre-dive millivolt checks were good and O2 cal on surface was good. Did the first dive and noticed the cell reading higher, but at depth the cell came back in line with the other two. Next dive decided to to do the 6m O2 flush and whamo cell nbr 3 was non linear. Cells one and two were reading 1.4 and climbing. Cell nbr three never made it to .95 and was promptly voted out. I changed the set point to .7 and went to 50 fsw and cell three was back in line with the other two cells. I watched the cells like a hawk for the remainder of the dive with my OC buddies. After the dive I ordered new cells and replaced the faulty one and now have a spare. So yes cells can go high then current limit all in one day.

    The main things are keep alert, know your equipment, follow your training and don't be afraid to call the dive.

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    Re: Serious incident (hyperoxia) when 2 cells fail simulatenously and identically

    Quote Originally Posted by Nuclear Penquin  View Original Post
    In the event all my cells failed, I can rely on my HUD to maintain my ppo2,

    Ummmmm, are you for real?

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    Quote Originally Posted by Packhorse  View Original Post
    Ummmmm, are you for real?
    He said he dives a meg. Hopefully he has had more training than watching it be destroyed at 250'.

    He has to mean if the displays fail on his handsets..


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    Any info on how the cells were stored / treated before the dive? Could there be something that had happend to them that made them go current limited at the same time?

    The reason I ask is that I was at a dive site this summer, when another diver had the same problem, though he identified it on a 6m O2 flush. His cells were from different batches.

    If everything was just a normal probability percent this would be rare, but if heat/cold/moisture etc in storage is affecting, then I guess it is not that low probability anymore. Actually, then it is not impossible that all 3 cells fail at the same time.

    /Jonas

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